In order to connect to a wireless cellular system such as high-speed packet access (HSPA) and long-term evolution (LTE), the user equipment (UE) conventionally searches for signals transmitted by network (infrastructure) entities such as base stations (BSs) or transmitter-receiver points (TRPs). The term TRP is used herein to refer to any network component or network controller such as a base station or access point.
The first signals acquired and detected by the UE are called synchronization (sync) signals whose role is to communicate important information to the UE, e.g., a cell identifier (ID), symbol and frame timing information, etc. A sync signal in this disclosure may refer to a set of one or more signals that communicate such information and may or may not occupy consecutive time and/or frequency resources. An example is the long-term evolution (LTE) system where a sync signal is composed of a primary sync signal (PSS) and a secondary sync signal (SSS), which may or may not occupy successive symbol times depending on the system configuration. Once a UE obtains such information by detecting a sync signal from a TRP, it can initiate a connection procedure to the TRP.
Due to mobility and other phenomena impacting the channel quality, a UE may need to connect to, or benefit from connecting to, another TRP while staying connected to the same network. This procedure is called handover. For this purpose, a UE maintains a list of potential handover destinations and their channel quality by continuously listening to the wireless medium and detecting sync signals from nearby TRPs. This information can be reported to the network through the TRP currently serving a UE. The network or the UE can then decide whether and when a handover is necessary or beneficial.